WASHINGTON — John F. Kelly, President Trump’s homeland security secretary, on Sunday defended a reported effort by Jared Kushner, the president’s embattled son-in-law and key adviser, to establish a secret channel with Russia during the transition, calling it “a good thing.”

“Any information flow into the government and then considered by the government, I won’t criticize that,” Mr. Kelly said in an interview on ABC’s “This Week.” “All of these lines of communication are a positive thing, in my opinion.”

Mr. Kelly’s remarks came amid news that Mr. Kushner was a focus of investigations into possible collusion between Russia and Mr. Trump’s associates during the campaign and transition, a development that has consumed an already-beleaguered White House.

The president, home again after a nine-day trip overseas, quickly turned his Twitter account back into a political weapon on Sunday, assailing what he called the “fabricated lies made up by the #FakeNews media.”

Mr. Trump’s administration has been straining to contain the fallout from news reports that Mr. Kushner spoke in December with Russia’s ambassador, Sergey I. Kislyak, about establishing a secret channel to Moscow to discuss the war in Syria and other matters.

In television interviews on Sunday, Mr. Kelly defended Mr. Kushner’s conduct and his character generally.

“He’s a great guy, decent guy. His No. 1 interest, really, is the nation,” Mr. Kelly said on NBC’s “Meet the Press.” “So, you know, there’s a lot of different ways to communicate, back channel, publicly with other countries. I don’t see any big issue here relative to Jared.”

Mr. Kelly also echoed Mr. Trump’s aggressive posture against leaks, calling American officials’ disclosure of information about last week’s bombing in Manchester, England, “darn close to treason.”

Soon, Mr. Trump had fired off a message of his own on the subject.

“British Prime Minister May was very angry that the info the U.K. gave to U.S. about Manchester was leaked,” he wrote on Twitter. “Gave me full details!”

It was a familiar morning for Mr. Trump on his favored medium — and for a nation that had, for a little more than a week, gone without the president’s stream-of-consciousness missives.

The president had largely avoided provocative Twitter posts during his journey through the Middle East and Europe, but he quickly returned to form after arriving at the White House late on Saturday, pushing back on Sunday morning against the flurry of news reports about Mr. Kushner.

“Whenever you see the words ‘sources say’ in the fake news media, and they don’t mention names,” Mr. Trump wroteon Twitter, “it is very possible that those sources don’t exist but are made up by fake news writers. #FakeNews is the enemy!”

The president woke up to find headlines and television talk shows focused on the latest turns in inquiries that he had been able to put aside for much of his trip. The freshest developments brought the matter into his own family.

News articles also focused on efforts by administration aides to develop a damage control plan to handle the controversies. That plan would potentially seek to wall off questions involving the investigations from day-to-day governing by creating a separate war room in the White House, assembling a high-powered legal team outside the White House and shaking up the president’s communications team.

Aides expected Mr. Trump to begin meeting with lawyers as early as Sunday to talk about a way forward, but one consensus among administration lawyers and private lawyers consulted by the White House in recent days was that Mr. Trump needed to restrain himself on Twitter, rather than create new problems with impulsive or unfiltered messages.

Mr. Trump demonstrated during his travels to Saudi Arabia, Israel, the West Bank, the Vatican, Belgium and Italy that he could be disciplined about his use of social media. Over the nine-day trip, he or his aides used the president’s Twitter account to promote his foreign and domestic policies, thank his hosts and otherwise stay on message.

But he seemed on Sunday to be as aggrieved as ever by what he considers unfair news coverage. “It is my opinion that many of the leaks coming out of the White House are fabricated lies made up by the #FakeNews media,” he wrote on Sunday morning.

If Mr. Trump continued his television-watching habit on Sunday, it was unlikely that his mood improved.

Representative Adam B. Schiff of California, the top Democrat on the House Intelligence Committee — which is conducting one of the investigations into possible ties between Trump campaign and Russia — repeated some Democrats’ calls for a review of Mr. Kushner’s security clearance.

If the reports that Mr. Kushner had discussed a secret channel were true, Mr. Schiff said, “it’s obviously very concerning.”

“You have to ask,” he said on ABC’s “This Week,” “well, who are they hiding the conversations from?”

James R. Clapper Jr., who was until January the director of national intelligence, said that although he had not seen “any smoking-gun-certitude evidence of collusion” by the time of his departure, his antenna was up.

“My dashboard warning light was clearly on,” he said on “Meet the Press.” “And I think that was the case with all of us in the intelligence community, very concerned about the nature of these approaches to the Russians.”

The president did receive a measure of cover from some congressional Republicans, who declined on Sunday to criticize Mr. Kushner’s behavior.

Senator Bob Corker of Tennessee, the chairman of the Foreign Relations Committee, said Mr. Kushner “has said that he’s more than willing to answer any and all questions.”

“They reached out to us yesterday to make sure that we knew that was the case, and I’m sure he’s willing to do so,” Mr. Corker added on “Meet the Press.”

And Senator Lindsey Graham of South Carolina registered his skepticism over the reports themselves.

“I don’t trust this story as far as I can throw it,” he said on CNN’s “State of the Union.” “I think it makes no sense that the Russian ambassador would report back to Moscow on a channel that he most likely knows that we’re monitoring. The whole story line is suspicious.”

The Washington Post was first to report last week on Mr. Kushner’s suggestion to the Russian ambassador, and three people informed about it confirmed it to The New York Times.

Mr. Trump, punching away on Twitter, was eager to move on to other subjects.

He singled out last week’s special election in Montana for an open House seat that the Republican candidate, Greg Gianforte, won the day after he was charged with misdemeanor assault in an attack on a reporter. Mr. Trump made no comment about Mr. Gianforte’s actions, complaining instead that Republicans did not receive more credit for winning a district that the party has held for 20 years.

“Does anyone notice how the Montana Congressional race was such a big deal to Dems & Fake News until the Republican won?” he wrote.

A version of this article appears in print on , on Page A12 of the New York edition with the headline: Trump Official Defends Kushner’s Reported Talks With Russia as ‘Good Thing’. Order Reprints | Today’s Paper | Subscribe